Alfa Romeo Forums banner

1 - 19 of 19 Posts

·
Registered
Joined
·
113 Posts
Discussion Starter #1
I have been trying to synch my carbs for the last week and they seem to have a mind of their own. I followed various instructions posted on the ABB along with various publications; yet it just doesn't happen! The engine keeps rocking side to side. In the Brookland service manual, they tell us to disconnect the throttle linkage and back off the idle screw and the synch screw almost all the way out. Then it tells us to push down on the rear carb throttle lever to make sure the linkages are free. Then screw in the synch screw until it touches the throttle plate of the other carb. Then screw in the idle speed screw until it touches the carb throttle lever and add an extra 1/2 turn. Then attach and adjust the throttle link but adjust it just enough to give it a pre-load on the carb throttles. This sounds pretty straight forward. However, there are other publications that does not mention anything about disconnecting the throttle linkages. I did however notice that the linkage ends on my car are very look and sloppy. When I set the synch., I can disconnect the linkage ends with ease. After doing so, there is absolutely no change in the carb's RMP. I also noticed that the bell crank ball is also loose. There is in and out play in the pivot ball where the carb center link connects to. Is this enough play that would hinder the carb synchronization???
 

·
Super Moderator
Joined
·
12,189 Posts
There are any number of factors that figure in to Weber balance. They are Webers? Linkages all wear loose and sloppy with time. Bigger issues are the divot that forms in the center connecting link. This will slightly change location with butterfly bar movement. It can be replaced or repaired. Next is engine tune. If you have odd valve clearances, a loose timing chain , bad plugs or ignition problems, low compression on one or more cylinders, nothing you do with Weber balance will help.
Finally, if the Webers have incorrect float levels, or are gummed up, or full of rust from the fuel tank, you have Weber problems. All these things conspire to make for balance problems.
Generally, rule #1 is, if it starts to run oddly, DON"T fool with the Webers. Look elsewhere. They do not just go out of balance or tune, unless due to wear, or dirt.
As I rebuild Webers for BB customers, I've seen some that really need help. These came from Keith Goring, before and after. They'll run good now!
 

Attachments

·
Registered
Joined
·
415 Posts
First, Mr. Raymond - do you have any idea of the kinds of sentences being imposed these days for the willful distribution of carburetor porn over the intertubes? You are one brave man, I must say (incidentally - that is a beautiful pair).

Nitrokid - when you're checking all that GR has offered.. on the topic of "ignition" - I was messing with my carbs ..FOREVER.. until I discovered that my idle timing was all over the (advance) map. Some dizzy cleanup and, mainly, fresh advance-weight springs, suddenly made everything consistent enough that the carbs could ..FINALLY.. be adjusted for decent, consistent tune. Just a data point.

Good luck.
 

·
Registered
Joined
·
4,294 Posts
Syncronizing Webers is one of the black arts of Alfadom. I once drove my GTV around for months trying to learn how to get the carbs right. I'd stop, take out my extra long screwdriver (you have one of those right?) make a adjustment, drive a bit, and do it again. Finally I reached the magical point where I could adjust Webers by ear.

Along the way I found that Webers are very robust carburetors and will work well even when it looks like they shouldn't. For security, you can always buy new ball ends for your linkage but, honestly, I've never seen linkages so worn they effect the carbs sync.

Although you'll get street cred by adjusting Webers by ear, a much, much simpler (and more accurate way) is to invest in a "Syncrometer" air flow measuring tool. These are avaliable all over the net. Buy one of these along with the cool curved rubber adaptor and you'll be able to get a much more accurate syn in just a few minutes. Follow the instructons for setting idle air, timing, etc. and you're done. Unless, of course, you have a problem with the carbs or the rubber mounts but that's a different question.
 

·
Super Moderator
Joined
·
12,189 Posts
Jim, You are absolutely correct. I STILL have my "special (real crummy) long Weber screwdriver" almost 50 years later. When I go for extended driving trips in either my AUSCA spider or 275 GTB Ferrari, that screwdriver goes with me! I do it all by ear and feel, but really like that old tool. Perhaps it just vibrates just right. Even my 14 year old son knows which tool to reach for when I say "...the Weber screwdriver".
 

·
Premium Member
Joined
·
14,957 Posts
Hey Nitrokid,
The set-up procedure that you quoted is the same one that is in the AR workshop manual and it is the one that I use. I don't mess with synchrometers and the like. A few years ago, I bought a Dwyer Magnehelic differential perssure gauge with the intention of using it to get the synchronization dead nuts, but I have not used it because it is not really necessary. I agree with the poster who told you to make sure that your ignition, compression and valve timing are good. Then look at the spark lug plugs. Are they white, brown, black or oily?
 

·
Registered
Joined
·
4,294 Posts
C'mom guys, there are better ways of paying your dues than this.:)

The Syncrometer is so easy to use and so accurate that just about anybody can spend a few minutes and get a wonderfully smooth idle. Professional mechanics use these (but only when there are no customers around).
 

·
Premium Member
Joined
·
14,957 Posts
The Alfa Romeo Manual method has worked from long before synchrometers were available.
 

·
Trained (ex)Professional, , 1953-2018 RIP
Joined
·
16,232 Posts
What's a syncrometer? ;)
 

·
Registered
Joined
·
4,294 Posts
Syncrometer.

Note: This is the passive version. Used with the proper curved rubber mount it fits neatly inside the plenum of an Alfa and does a good job of accurately measuring air flow between the two carbs. Of course, there's also the steam-powerd version that is even better, although it is a bit more costly and requires special training and an assistant to stoke the boiler. :)
 

Attachments

·
Registered
Joined
·
116 Posts
have had a sync meter like the one shown and it has done hundreds of carbs over 25+ years.make sure that the carbs are both attatched to the plenium as they must be supported together when synced . good luck
 

·
Registered
Joined
·
561 Posts
Syncrometer
I used to have competions with a co-worker in a Alfa workshop to see who could get cars running smother: Me with the trusty $100 synchrometer (and a piece of shaped radiator hose to fit into the airbox), or him with the ridgy-didge genuine Alfa mercury nanometer (whatever).... Results: Dead heat, but mine was heaps easier and faster!
 

·
Registered
Joined
·
561 Posts
A couple of other tips for any interested:

As a baseline when you have rebuilt the carbs, had them off or some idiot had stuffed it all up: Take the idle progression caps off (big round screws over the butterflies), look down with a torch and see if they are lined up side to side as you open the throttle. Adjust so they are.

And when you are making the final adjustment: Don't just the centre throttles to each other. Check that all the outers are matching the inner throats. You can adjust this on some carbs via the bypass, and on ones without a GENTLE twist of the shaft will get them perfect. Then rebalance side front to back etc.
 

·
Registered
Joined
·
415 Posts
What's a syncrometer? ;)
A fancy version of this classic:



Which is what real men use - or at least those delusional enough at one time to think that English products defined sporty cars. Truthfully, there was something about the simplicity of an SU carb's operation that I always admired. (Except for the cold-start enrichment system, the linkage of which can only be adequately described by that very British term, "ghastly".)

Note that "Uni-Syn" can aptly be translated to the oxymoron "single synchronization".

Plexiglass-tube-and-glued-rubber-grommet "Weber" adapter shown is sold/constructed separately. Some of us never learn. "Hey, if it doesn't work with the carburetors it was designed for, maybe it will work on others." In fact, I'm pretty sure I made the adapter for the downdraft Zeniths on an MBZ 250C (inline 6) I had, and then found it also fit the Alfa's Webers.

And while leaving an Alfa airbox attached won't fly, a Uni-Syn's foam rubbery gasket seals on SPICA throats, too. In my case, Uni probably means universal.
 

·
Registered
Joined
·
113 Posts
Discussion Starter #15
Problem solved.
Turns out it was the throttle linkages and the bell crank.
I made up some new throttle linkage rods and ordered socket ends from Joe at Centerline. As I replaced the ends I noticed that one of the link end balls on the bell crank had cracked and the ball was very loose. I put a spot weld on it, put a fiber washer behind the C clip that holds the bell crank to the engin block to pick up any forward movement on the pivot pin. Set the synch. then the mixture and low and behold, we have lift off!!
Thanks to everyone who contributed.
 

·
Registered
Joined
·
415 Posts
[..] seen linkages so worn they effect the carbs sync. [..]
I do have one final, interesting note after a recent "carb renovation + adjustment" odyssey. After finding virtually every problem ever described here re: DCOEs (down to the throttle plates needing re-centering and dry throttle shaft bearings) and remedying each one as best I could, I adjusted it all.. and still couldn't get the balance right.

I finally realized that a combination of a very slightly bent ref. tab on the rear carb's throttle lever, and a dimple worn into the tab's surface was resulting in the synch screw bottoming out against its spring. I replaced the screw with one 2mm longer and ..viola.. the front carb's throttle plates could now catch up with the rear's. Why I didn't notice the screw starting to bind/tighten is another question.

Removing the progression hole inspection cover screws to "view" each carb's initial throttle plate position through the first hole was invaluable in diagnosing this.

Clayton105 - there's a pint waiting for you in SF for pointing out this (..almost obvious, once you think about it..) trick here, earlier. Thanks!
 

·
Registered
Joined
·
521 Posts
A fancy version of this classic:



Which is what real men use - or at least those delusional enough at one time to think that English products defined sporty cars. Truthfully, there was something about the simplicity of an SU carb's operation that I always admired. (Except for the cold-start enrichment system, the linkage of which can only be adequately described by that very British term, "ghastly".)

Note that "Uni-Syn" can aptly be translated to the oxymoron "single synchronization".

Plexiglass-tube-and-glued-rubber-grommet "Weber" adapter shown is sold/constructed separately. Some of us never learn. "Hey, if it doesn't work with the carburetors it was designed for, maybe it will work on others." In fact, I'm pretty sure I made the adapter for the downdraft Zeniths on an MBZ 250C (inline 6) I had, and then found it also fit the Alfa's Webers.

And while leaving an Alfa airbox attached won't fly, a Uni-Syn's foam rubbery gasket seals on SPICA throats, too. In my case, Uni probably means universal.
I've been using a Uni-Syn without any modification or added tube. It covers the throat and seems to work fine. Am I missing something here?
 

·
Registered
Joined
·
415 Posts
I've been using a Uni-Syn without any modification or added tube. It covers the throat and seems to work fine. Am I missing something here?
I should have clarified. On my only Weber'd car (105.2/Giulia Sprint GT), the mounting studs attached to the carb, adjacent to each throat (for the OE airbox) forces the Uni-Syn's opening way off-center to the very edge of the intake bore. Since the "vacuum intake" hole for the Uni-Syn is at 3 o'clock, it's nearly covered at 2 of the 4 throats.

It just so happened that the plastic adapter (1-3/4" OD plastic tube w/ RTV'd rubber grommet) I made for the MBZ's downdraught Zeniths fits the 40DCOEs' aux. venturis perfectly, with the 2" length tube extending the sealing face of the Uni-Syn out past the ends of the studs, allowing an easily achieved, centered/upright orientation.

But if the carbs' intake face has no studs attached, no adapter would be needed.
 

·
Registered
Joined
·
521 Posts
I should have clarified. On my only Weber'd car (105.2/Giulia Sprint GT), the mounting studs attached to the carb, adjacent to each throat (for the OE airbox) forces the Uni-Syn's opening way off-center to the very edge of the intake bore. Since the "vacuum intake" hole for the Uni-Syn is at 3 o'clock, it's nearly covered at 2 of the 4 throats.

It just so happened that the plastic adapter (1-3/4" OD plastic tube w/ RTV'd rubber grommet) I made for the MBZ's downdraught Zeniths fits the 40DCOEs' aux. venturis perfectly, with the 2" length tube extending the sealing face of the Uni-Syn out past the ends of the studs, allowing an easily achieved, centered/upright orientation.

But if the carbs' intake face has no studs attached, no adapter would be needed.
That 'splains it. Mine have only the bottom studs in place.
 
1 - 19 of 19 Posts
Top